The Transgenic Mouse Shared Resource is a fully Cancer Center-managed facility. The generation and use of transgenic and gene-targeted mice is an essential technology for basic cancer research. Since its establishment in 1995 the Transgenic Mouse Shared Resource has served to make transgenic technologies accessible to all Cancer Center members, which has had a major impact on the quality and quantity of cancer research using genetically modified mouse models. The resource has served over 80 different investigators over the past three years, and has generated hundreds of new strains of transgenic and gene-targeted mice. The services provided by the Transgenic Mouse Shared Resource are: Production of transgenic mice by pronuclear DMA microinjection and embryo transfer; Production of chimeric mice by blastocyst injection of genetically modified ES cells and embryo transfer, which is part of the procedure of producing knockout or knockin mice; and Gene targeting, which involves the electroporation of a targeting vector into pluripotent mouse embryonic stem (ES) cells and the selection of gene-targeted clones; Education of investigators and advice on vector and experimental design for experiments using transgenic and knockout mice. The facility maintains a library of vectors and genes that are generally useful for the construction of transgenes and targeting vectors. In the future, to supplement these now standard transgenic methods, we plan to establish a service that will use "BAG recombineering" to efficiently produce large-insert gene targeting vectors and transgenes. Beyond these specific fee-based services, the Resource provides free advice and consultation on all aspects of the design, generation, breeding and analysis of genetically modified mouse models. The Director (Dr. Frank Costantini), Co-Director (Dr. Thomas Ludwig) and Manager (Dr. Chyuan-Sheng Lin) of the facility collectively have many decades of experience in numerous aspects of mouse genetics, transgenic mo'use technology, and the use of mouse models in cancer research, and their expertise has contributed greatly to the excellence of transgenic mouse research at Columbia. During the last period of the CCSG, 51% of the investigators using the facility were Cancer Center members with peer-reviewed funding, with those members representing from 53% to 78% of the usage of the 3 available services. The proposed total operating budget of the facility is $531,018 for the Transgenic Mouse Shared Resource, of which we are requesting $183,948 from the CGSG. In addition, mouse cage costs managed by the Institute for Comparative Medicine are $324,111, of which we are requesting $135,771 from the CCSG.